Recording process



1963 R. F. BARTLETT ETAL 3,414,410

RECORDING PROCESS Filed April 15, 1964 2 Sheets-Sheet 1 lNvENToRsRICHARD E BARTLETT CARL FW. E/(MAN JUL/ETTE I. P/A BY M, 7 1mm 1ATTORNEY Dec. 3, 1968 RECORDING PROCESS Filed April 15, 1964 R. F.BARTLETT ET AL 2 Sheets-Sheet Z I I! I QED 1 RICHARD E BARTLETT CARL EW. EKMA/V UL/ETTE E R/AN 4mm MW ATTZRNEYS United States Patent 3,414,410RECORDING PROCESS Richard F. Bartlett, Lexington, Carl F. W. Ekman,Bedford, and Juliette F. Plan, Burlington, Mass., assignors to ItekCorporation, Lexington, Mass., a corporation of Delaware Filed Apr. 15,1964, Ser. No. 359,956 14 Claims. (Cl. 96-27) ABSTRACT OF THE DISCLOSUREA dye-sensitized copy medium comprising a photosensitive semiconductoris exposed to an image pattern of radiation which desensitizes thedye-sensitized medium to activating radiation in those portions whichare struck by this desensitizing radiation. This thus-imaged copy mediumis then uniformly exposed to activating radiation to activate thoseportions of the copy medium which remain sensitive to this radiation.The activated portions of the copy medium are then developed bycontacting with suitable image-forming materials.

The present invention relates to data reproduction, and relates inparticular to methods and apparatus for directly making positive printsof images to be reproduced.

Commonly owned copending application Ser. No. 199,211, filed May 14,1962 by Berman et al. and incorporated herein by reference disclosesmethods for producing images in a copy medium comprising photoconductivematerials by exposure of the copy medium to an image pattern ofactivating radiation to render chemically reactive those portions of thephotoconductor medium which are struck by the activating radiation. Theactivated irradiated medium is next contacted with a developer to effecta chemical redox reaction between the developer and the activatedchemically reactive portions of said medium on such contact.

For example, according to the invention of the copending application, acopy medium comprising finely-divided titanium dioxide, such as a TiOfilled or coated paper, may be exposed to light through an image patternto be reproduced. .Where light strikes the photosensitive oxide coating,the oxide becomes activated, i.e. chemically reactive. The medium issubsequently contacted with a developer system, for example including asolution of silver ion, which reacts at the chemically reactive portionsof the activated medium. Thus, for instance, silver ion reacts toprecipitate metallic silver. The exposed medium may be developed bycontacting it with a developer system which tends to deposit solidswhere solids are already present on the medium. Such systems amplifyfaint or invisible images and render them visible. A typical developersystem for image amplification, for example, is one in which a metal ionsuch as silver or mercury is present together with a material forming aredox system, such as hydroquinone. With such a developer system,relatively heavy deposits of metal will be formed on the medium in thoseportions which have been illuminated and which comprise chemicallyreactive activated TiO resulting in the direct formation of a visibleimage in the copy medium on contact with the developer system.

Images formed according to the technique just described will be negativeimages, that is opaque portions will form in the print in lightstruckareas, i.e. those corresponding with translucent areas in the imagepattern to be reproduced. Thus, unless a negative of the image desiredto be reproduced is first made and employed as the image pattern throughwhich the copy medium is exposed, prints obtained according to theprocess just described will be negatives of the desired image.

3,414,410 Patented Dec. 3, 1968 According to the present invention,certain dyes known to the art and commonly used as sensitizers in silverhalide photography are used for the treatment of photoconductivematerials in preparing copy media for a process which permits the directproduction of positive prints of good quality. In particular, the dyesplay a dual role as both sensitizers and desensitizers for thephotoconductive mateirals treated.

According to the present invention, positive prints are made employing acopy medium in which one or more sensitizing dyes are present in atleast a monomolecular layer atthe surface of a photoconductive materialpresent in said copy medium. Suitable photosensitive materials includeelements and compounds such as Ge, TiO ZnO, ZI'Og, S1102, Bl2O B60,$13205, T3205, T602, B203, ZnS, and SnS for example. Many of thesematerials are photoconductive compounds of metals with non-metals ofgroup VI-A of the Periodic Table, for example metallic oxides andsulfides.

The medium comprising a dye-sensitized photoconductor is exposed to animage pattern of activating radiation for a period of time dependent onthe type of dye used and the light source but commonly averaging aboutthree or more minutes in length, for example, when a low inten sityincandescent source is employed. During earlier portions of thisexposure, the dye may act as a photosensitizer for the photoconductivematerial, facilitating transfer of the incident radiant energy to thematerial in a manner known in the arts relating to the dye sensitizationof lightsensitive pigments of this type, thereby activating the materialin exposed portions. However, on extended ex posure to radiationaccording to the methods of the present invention, the dye-treatedmaterial becomes increasingly insensitive to further irradiation andbecomes relatively less activated.

This desensitization or deactivation effect is shown in FIG. 1 of theaccompanying drawings. In FIG. 1, the printability or degree ofactivation of a copy medium comprising a typical dye-sensitizedphotoconductive material is plotted in arbitrary units on the ordinateas a function of the time of exposure to an activating light sourceplotted on the abscissa. The printability of the medium rapidly reachesa maximum, then typically decreases in a manner not heretoforerecognized by those skilled in the art.

The relatively long image exposure mentioned above as a first step inthe method of the invention should preferably be of such length asreduces the printability of the activated or lightstruck portions of themedium to at least one half of its maximum value on a plot similar tothat shown in FIG. 1. The photoconductivity in air of a dyetreated copymedium is one measure of its printability, and will typically follow acurve like that shown in FIG. 1.

After the image exposure resulting in a deactivation randdesensitization of light-exposed areas, the dye-treated printing mediumis next uniformly illuminated by exposure to a light source for a shorttime period, commonly averaging about three seconds when a low intensityincandescent source is employed, for example, so that the medium is inthe range of maximum printability as shown in the typical plot ofFIG. 1. Those portions of the printing medium not previously struck bylight during said first exposure to an image pattern of desensitizingradiation are relatively more light sensitive, and the dye coating inthese areas assists in the activation of the sensitive photoconductor torender it reactive with oxidizing and reducing agents used asdevelopers. On the other hand, those portions of the printing mediumwhich have previously been exposed to an image pattern of radiation fora long period of time have become desensitized, and are not activated toa great degree by the short uniform second exposure.

Thus, it will be seen that those portions of the twiceexposed printingmedium which remain activated, i.e. are left chemical-1y reactive by thetwo exposures just described, correspond with opaque portions of theimage to be reproduced. On development, these activated portions of theprinting medium can be rendered opaque, for example by contact withsilver ion to form visible deposits of metallic silver, so that apositive print of the original image results.

A number of developing techniques suitable for use in the presentinvention are disclosed in copending application Ser. No. 199,211. Forexample, development may occur in a single step by first contacting thetwice-exposed medium with a developer such as a solution containing ametal ion reducible to free metal on such contact, e.g. silver ion ormercury ion, which are respectively reduced to free silver and mercuryon contact with activated portions of the medium. However, a high degreeof surface activation is generally required for production of a visibleimage in this manner. It is more convenient to develop the exposedmedium using an image-amplifying developer system of the type discussedearlier herein. In one such process, a developer is first employed toform a latent developed image in the medium. That is, the twiceexposedmedium is developed (e.g. by contact with silver ion) to produce aninvisible image (e.g. a fine invisible deposit-of metallic silver)therein. In a later second step, the developed image invisibly presenton the medium may be made visible by contact with a developer bringingabout image amplification. Such developers, as known in the art ofsilver halide photography for example, suitably comprise a metallic ioncombined with a redox system such as of hydroquinonequinone and areformulated to tend to deposit a metal such as silver on sites wheresilver is already present. Thus, a latent developed silver imageproduced according to the positive printing process of the presentinvention can be made visible by such development with amplification.

More simply, such an amplifying developer system may be used to producea visible image directly in the exposed medium in a single step, withoutprior development of a latent developed image.

In general activation of the photoconductive materials contained in thecopy media of the invention makes the materials chemically reactive withoxidizing agents which are at least as easily reduced as copper ions,e.g., copper, mercury, silver, gold and other noble metals, as well asorganic materials such as methylene blue.

FIG. 2 of the accompanying drawing shows a system for producing positiveprints according to the present invention. FIG. 2 shows imaging means 11comprising activating radiation source 12, image object 13 such as aphotographic transparency, and conventional optical means 14 forfocusing an image pattern of radiation on copy medium 15, which latteris dye sensitized according to the present invention. In the apparatus,copy medium 15 is suitably transported by conveying means 16 shown inFIG. 2 as a belt and roller system, though other suitable conveyingmeans will be apparent to those skilled in the art. After exposure to animage pattern of radiation, copy medium 15 is next uniformly illuminatedby exposure to radiation source 17 (shown with the medium f in position15a). Conveying means 16a by which copy medium 15a is transported to andfrom source 17 may be the same as means 16, or may be distincttherefrom,

aqueous solution of silver nitrate. On emergence from bath 18, themedium will have formed thereon a latent (i.e. invisible) silver imagewhich is suitably amplified by further development in bath 19 (positioncomprising, for example, a solution of quinone-hydroquinone. Thepresence of the redox system furnished by bath 19 causes further ionicsilver, adhering to copy medium 15b on emergence from bath 18, todeposit as metallic silver on those portions of the medium where :alatent image comprising invisible deposits of metallic silver priorlyexisted. Bath 19, thus, effects an amplification of the latent image,and renders the latent image visible. Finally, copy medium 15d having avisible silver image therein is transported to bath 20, suitablycomprising water for washing, and/or other fixing and stopping agents.In FIG. 2, as for conveying means 16 and 16a, conveying means 21 fortransporting copy medium 15a-15d through baths 18, 19, and 20 maycomprise a single continuous con veying system, or two or moreindividually controllable and regulable conveying means.

The dyes employed for treating the photoconductive insulating pigmentsof the invention are, in general, those heretofore used in thephotograhic arts for sensitizing silver halides (cf. The Theory of thePhotographic Process by C. E. Kenneth Mees, the Macmillan PublishingCo., New York, Revised Edition, 1954) or materials such as zinc oxide,to render them sensitive to and activatable by light of Wavelengthsother than those to which the untreated material would be sensitive.Normally, dye sensitization extends the usual ultraviolet sensitivity ofthe untreated photoconducting substrate to longer wavelengths such asthose in the visible. The dyes include acridine dyes such as AcridineOrange, thiazine dyes such as Methylene Blue, phthaline dyes such asRose Bengal and Eosin Y, triphenylmethane dyes such as Malachite Green,or Crystal Violet, and cyanine dyes such as kryptocyanine, neocyanine,dicyanine, and pinacyanol.

The dyes may be used in solution to treat the Photoconductive materialsprior to their incorporation into a copy medium. The dyed pigments canbe simply deposited on a substrate, or can be incorporated into asubstrate such as the fibrousweb of paper. Alternatively, the dye can becombined with the photoconductive materials in the copy medium, forexample by dispersion of the dye in the same resin commonly used to bindphotosensitive pigments to a suitable insulating or conductive backingsuch as wood, glass, paper, or metal.

The cyanine dyes, including the simple cyanines, carbocyanines, :andhigher cyanines, are particularly preferred for use in the presentinvention since they promote maximum differences in activity betweenthose areas of the copy medium in which the photoconductive material hasbeen desensitized by a first extended exposure to an image pattern ofradiation and those portions containing photoconductive material whichis first activated by the later uniform exposure.

Another technique for improving discrimination in the print is darkadaption of the copy medium after the first imaging exposure. This isparticularly desirable where the imaging radiation tends to activate thephotoconductive insulating pigment even in the absence of sensitizingdyes. For example, the exposure of dye-sensitized titanium dioxide toimaging light from a tungsten lamp causes the printability of a copymedium containing the same to behave in a manner suggested by FIG. 1 ofthe drawings. The insensitivity of exposed portions of the TiO tosubsequent radiation is consistent with a destruction of the sensitizingdye where extended exposure to light has taken place, or with some otherinterference with the capacity of the dye to transfer energy to thepigment. The underlying titanium dioxide pigment, once the dye isincapacitated by the imaging exposure, cannot be activated to asignificant extent by a second exposure to a tungsten source, since itis now substantially insensitive to the incident radiation in thoselightstruck areas where the sensitizing dye no longer sensitizes.

On the other hand, if ultraviolet light is used for the imagingexposure, to which light the titanium dioxide pigment underconsideration is sensitive even in the absence of sensitizing dye, theunderlying pigment tends to become activated and to remain activated forsome time after exposure, even though dye may be destroyed or otherwiseincapacitated by the exposure employed. In the latter case, it isdesirable to dark adapt the copy medium after the first exposure inorder further to deactivate the medium.

Dar-k adaption may be effected in a literal manner by permitting thecopy medium to remain in the dark, for example, for periods of from 1224hours, at room temperature. With increasing periods of time, the firstexposed portions of the medium become less and less apt to react withdeveloping agents after the second uniform exposure to which the mediumis next to be subjected. Hence, maximum contrast is obtained between theportions of the medium activated by such a later uniform exposure andthose portions exposed and deactivated during the prior imagingexposure.

Alternatively, dar-k adaption may be effected more rapidly by heating ofthe exposed copy medium at temperatures below the decompositiontemperature of the dyes present. Forjexample, the copy medium can beheated gently in the dark in an oven arrangement at about 250 C. forperiods up to a minute or more, for example. It may be convenient tosubject the exposed medium to hot air from a blower. Temperatures ofabout 300C. are commonly generated by such blowers, and exposures tosuch temperatures for as little as seconds will help speeddesensitization of the medium.

Finally, the exposed copy medium can be dark adapted by exposure to acorona discharge, for example by passing the spark from a Tesla coilover the surface of the medium. This technique has the disadvantage thatdye remaining in unexposed portions of the copy medium may be adverselyaffected by the corona discharge, perhaps by oxidation.

FIG. 3 shows another embodiment of apparatus according to the presentinvention in which dye-sensitized copy medium 31 prepared according tothe invention is exposed to radiation source 32 through image object 33and appropriate conventional optical means 34. Medium 31, conveyed bysuitable conveying means 35 is next transported to means 36 for darkadapting the exposed medium. Means 35, for example, comprises infraredsource 37, shown as an electric resistance heater. With its movementcontrolled by conveying means 35a, copy medium 31a is dark adapted foran appropriate time period. Next (position 31b) said copy medium isuniformly exposed to radiation source 38, and then developed. Medium31c, for example, can be directly contracted with bath 39 comprising adeveloper such as a metal ion in combination with a redox systemimmediately to produce a visible image on print 310 on contact with thedeveloper. Developed print 31d is next suitably contacted with bath 40comprising a fixing agent for silver ion, such as a soluble thiosulfatesalt. After fixing, p-rint 31e is water washed in bath 41. As for FIG.2, conveying means 43 transporting the prints through the developingstage may comprise a single conveying system, or two or moreindependently regulable and controllable conveying means.

Maximum discrimination in the prints produced by the techniques of theinvention is obtained when cyanine dyes are employed, and when some formof dark adaption is used to further desensitize those portions of thecoply medium struck by activating radiation during the first exposure toan image pattern of such radiation. However, the use of these dyesalone, or of some form of dark adaption alone, will also tend to givebetter prints.

For the second uniform exposure prior to developing, the copy medium issuitably exposed to a light source which will activate only thoseportions of the medium where dye is still present and which will leavesubstantially unaffected those portions of the medium where dye has beendestroyed or which have otherwise been rendered insensitive.Conveniently, the medium is exposed to visible light, which willactivate the previously unexposed dye sensitized portions, but will notaffect those portions of the medium where dye may have been destroyed bythe prior imaging exposure.

For both exposures, the time-intensity relationships well known in thephotographic arts are applicable, and specific exposure conditions canreadily be determined by anyone skilled in the photographic arts.

A better understanding of the present invention and of its manyadvantages will be had by referring to the following specific examples,given by way of illustration.

Example 1 A mixture of 4 parts by weight of titanium dioxide and 1 partby weight of an emulsion of Rhoplex acrylate resin containing about 50percent of solids in water was used to coat paper sheets.

A sheet of the coated paper was sensitized by dipping into a solutioncontaining 10 milligrams of neocyanine in ml. of methanol, and thendried.

The sensitized paper was exposed at a distance of about 4 inches toimaging light from a 25 watt tungsten bulb filtered to removewavelengths less than 460 millimicrons for periods of time between about3 minutes and 15 minutes.

The exposed sheets were immediately uniformly exposed to the same sourceof light for short time periods, of the order of 5 seconds.

The exposed prints were then dipped in a saturated solution of silvernitrate in methanol, and then in a solution comprising 1 gm. ofphenidone, 8 gm. of citric acid monohydrate, and 100 ml. of methanol. Apositive copy of the exposure image was obtained.

Contrast in the print was increased by permitting the copy medium tostand at room temperature in the dark for 24 hours after the imagingexposure and prior to the uniform exposure. Better contrast was alsoobserved if the copy medium was gently heated after the first exposure.

Alternatively, filled paper sheets containing about 20 percent ofphotoconductive ZnO or TiO pigment were prepared in conventional papermaking apparatus by addition of an aqueous slurry of the pigment to thebeater.

Finely divided water insoluble photoconductive pigments were also dyesensitized by contacting the pigments with dilute solutions ofsensitizing dyes. Excess dye solution was decanted, and the treatedpigments were dried. The pigments can suitably be deposited without abinder on a substrate such as glass, or can be incorporated into aplastic or the fibrous web of a paper, or can be dispersed in a bindersuch as sodium silicate or polyvinyl alcohol and used to coat rigid orflexible electrically insulating or conducting substrates.

Example 2 A number of TiO coated copy sheets like those of Example 1were treated by contacting them respectively with methanol solution ofthe dyes indicated below. After drying of the sheets, they were eachfirst exposed for 15 minutes to an image pattern of light from atungsten lamp as in Example 1, and then were given a 2 minute uniformsecond exposure. In each case, a positive copy of the image pattern wasobtained.

The dyes used were:

(1) Fuchsia-basic (pararosaniline chloride) (2) Orthochrome T(l,1'-diethyl-6,6-dimethyl-2,4-cyanine iodide) (3) Quinaldine Red (4)Diethyl thiocarbocyanine iodide (5) 3,3-diethyl-9methyl-thiocarbocyanineiodide (ll) ltttlplaayanine (l2) Dicyanine Although specific embodimentshave been shown and described, it is to be understood that they areillustrative, and are not to be construed as limiting on the scope andspirit of the invention.

What is claimed is:

1. A process for recording an image pattern of activating radiationcomprising (1) exposing a uniformly dyesensitized copy medium, said copymedium comprising a photosensitive semiconductor, to an image pattern ofradiation which at least partially desensitizes said dye-sensitizedmedium to activating radiation in those portions thereof which arestruck by this desensitizing radiation, and (2) then uniformly exposingthe selectively desensitized medium to activating radiation to activatethose portions of the medium which were not desensitized by the firstimagewise exposure, thereby making these portions capable of causingchemical reactions.

2. A process as in claim 1 comprising the additional step of contactingsaid copy medium with image-forming materials to produce a permanent,irreversible image in the portions of the copy medium activated by thesecond uniform exposure to activating radiation.

3. A process as in claim 2 wherein the image-forming materials comprisea liquid redox developer system.

4. A process as in claim 1 wherein the photosensitive semiconductorcompound is at least one compound of a metal with a non-metal of GroupVI-A.

5. A process as in claim 4 comprising the additional step of contactingat least the activated portions of the copy medium with a developersystem comprising silver ions.

diamino-S-phenyl phenazinium treg-te'g filergethod as in claim 1 mm isdesensitized b P mgn of visible light.

e met is a yanis d e. n Clam 6 Wherem cyanme y The method as in claim 1wherein said dye-treated medium 15 desensitized by exposure to an imagepattern of light destructive of said dye.

9. The method as in claim 1 wherein those portions of the medium struckby radiation during said first exposure to said image pattern ofradiation are deactivated prior to said uniform exposure to activatingradiation.

10. The method as in claim 9 wherein those portions of the medium struckby radiation during said first exposure are deactivated by storing themedium after said first exposure with the exclusion of activatingradiation.

11. The method as in claim 9 wherein those portions of the medium struckby radiation during said first exposure are deactivated by heating themedium at a temperature below the decomposition temperature of thesensitizing dye.

12. The method as in claim 1 wherein said medium comprises finelydivided particles of a solid photoconductive material insoluble in saidliquid redox system.

13. The method as in claim 12 wherein said photoconductive material is amember selected from the group consisting of semiconducting oxides andsulfides.

14. The method as in claim 1 wherein said photoconductive material istitanium dioxide.

wherein a cyanine dyey extended exposure to References Cited UNITEDSTATES PATENTS 5/1967 Hanson et al. 96-49 7/1967 Oliver 88-24

